When every gram lifted into orbit costs a fortune, “Reduce, reuse, and recycle” becomes more than just a trite saying. That covers everything, up to and including purifying liquid waste (ie, urine) into a more palatable beverage.

But recycling pee into water in space isn’t as easy as it is here on Earth. When the original Urine Processor Assembly went to the space station, it developed a “pee pancake,” a precipitate of that clogged up the system. The system needed to be modified to filter additional calcium ions: all that bone loss in microgravity resulted in astronauts peeing out double the normal concentration of calcium ions!